In monitoring the condition of a patient's heart, the systolic and diastolic blood pressures for each heartbeat are measured and recorded. The systolic pressure occurs when the heart contracts so as to cause positive peaks of increased pressure, and the diastolic pressure occurs when the heart relaxes so as to produce negative peaks of decreased pressure. These peaks have been identified in the following way. An ECG machine is coupled to the patient so as to provide at its output electrical signals that vary with the contractions and evaluations of the heart, and a QRS detector is coupled to the output of this ECG machine so as to produce a signal at the same point in each heart cycle. The peaks in the blood pressure signal are identified by correlating their time of occurrence with the signal produced by the QRS detector. Whereas this method works well, it requires signals for both blood pressure and ECG.